Stunted growth Cane toads could get a taste of their own medicine, with a chemical made by older tadpoles that disrupts development of younger members of their species.

"If we can identify the specific chemical and check very carefully that it doesn't have any effects on the native frogs, we could deploy it into ponds," says Dr Richard Shine, professor of biology at the University of Sydney and co-author of the paper published today in Royal Society Biology Letters.

Competition in ponds can be fierce. Cane toad tadpoles are known to hunt out and eat eggs from their own species, but may also have a more insidious way to dispose of any young upstarts.

Scientists suspected older tadpoles might slow the development of younger competitors by producing pheromones, chemicals that change the behaviour or physiology of other members of the species.

To test this hypothesis, the researchers placed cane toad eggs in containers split in half by flyscreen mesh. Ten of the containers contained older cane toad tadpoles on the opposite side of the mesh, and another ten were kept without tadpoles for comparison.

There was no physical contact between eggs and tadpoles, but waterborne cues could pass through the mesh. After 72 hours, the eggs hatched into tadpoles which were moved to other containers.

"To our astonishment, we got a very powerful effect from a short term exposure," says Shine. "The eggs hatched okay, but the tadpoles grew slowly and many of them died. If they survived to metamorphosis, they were about half the size of their unexposed siblings."

By the time they turned into toads, tadpole-exposed individuals had a survival rate 40 per cent lower than the others.

Species-specific cues

It is thought this chemical could be used against the toads, complementing existing measures like community cane toad musters. However, in the fight against this introduced species there is a need to ensure native frogs don't become collateral damage.

According to Shine, cane toad tadpoles communicate in a chemical language, using alarm pheromones that tell others to flee from danger, and attractant pheromones that say 'come over for a free meal.'

He says native frog species do not respond to these chemicals, so there's a good chance the development-disrupting pheromone would also be species-specific, though further testing is needed.